1. Field of the Invention
The present invention relates generally to a floating print head and an associated method for aligning the print head for thermal printing.
2. Description of Related Art
Thermal printers may be used to print a variety of configurations on substrates, such as cards and webs. A thermal printer typically includes a thermal print head having a row of resistors that may be activated to produce heat that is transferred to a print ribbon having thermally reactive ink or dyes and onto the substrate. One or more platen rollers is typically employed to transfer the substrate to print an array of rows to create an image or graphic, as well as to provide a support surface when the print head prints onto the substrate.
Given the increasing complexity of configurations printed on a substrate, such as images or graphics, the alignment of the print head becomes more important. It is desirable to have the line of resistors substantially aligned relative to the centerline of the platen roller to achieve a consistent print or dot line across the substrate. Because each of the multiple components that comprise the printer may have an associated tolerance, there is a greater probability of mismatching between the line of resistors and the platen as the tolerances stack up and make alignment difficult. Moreover, typical thermal printers do not allow for the print head to adjust once the print head is in a printing position, which makes realignment of the print head difficult, if not impossible.
Techniques have been developed to align the print head for thermal printing. For example, U.S. Pat. No. RE38,473 to Smolenski discloses a printer having a floating print head with alignment surfaces to position the print head. The print head is spring loaded to allow the print head to float in a vertical and horizontal direction within a lid assembly. In particular, the printer includes alignment posts having an oblique angle that corresponds to an angle on a print head alignment surface that compensates for linear and rotational misalignment. The print head includes a leaf spring, and as the print head is lowered, the print head alignment surface contacts a guide post alignment surface in the body of the printer. Because the alignment surfaces contact at oblique angles, there is a certain amount of tolerance in the approach positions between the alignment surfaces provided by the leaf spring. However, although the floating print head allows for translational and pitch alignment, the floating print head may not facilitate rolling adjustment about a longitudinal axis. As such, the Smolenski patent may not ensure that the line of resistors are both aligned relative to the centerline of the platen roller and that each of the resistors applies uniform pressure and thermal transfer across the substrate.
For these and other reasons, it would be advantageous to provide a floating print head assembly that is capable of applying uniform pressure across the substrate. Furthermore, it would be advantageous to provide a floating print head assembly that may compensate for tolerances inherent in the thermal printer assembly. It would also be advantageous to provide a floating print head assembly that is easily operated and assembled.